After spending almost 18 years in prison for a rape and murder he did not commit, Robert Dewey is likely to walk free on Monday. And the real murderer seems to have been identified.

Mr. Dewey, who was convicted in 1996 for the rape and murder of Jacie Taylor, in the western Colorado town of Palisade, will become the first person exonerated through Colorado's Justice Review Project, which was established in 2009 to review DNA evidence in cases where an innocent person may have been convicted. He is the 290th person in the United States to be exonerated by post-conviction DNA testing.

Dewey, a motorcycle enthusiast who goes by the nickname "Rider," is expected to walk free following a hearing in Grand Junction, Colo., Monday afternoon. On Monday morning, Dewey's attorney and the Mesa County District Attorney's Office filed a joint motion to vacate his earlier conviction.

"He’s overwhelmed, extremely excited; he’s anxious," said Jason Kreag, a staff attorney from the Innocence Project, a national nonprofit dedicated to identifying the wrongfully convicted. Mr. Kreag has been working on Dewey's case since 2008, along with Danyel Joffe, Dewey's personal attorney.

"I think that he like all of us can see the end is very near, and we expect within a few hours he’ll be totally free and the conviction will be gone. That’s just the start for him, but he’s ready," Kreag said.

The DNA testing that helped exonerate Dewey also led prosecutors to Douglas Thames, whose profile matches that of the semen sample from the crime. Mr. Thames is currently in prison for the 1989 rape and murder of Susan Doll, in Fort Collins, Colo. Prosecutors intend to charge Thames for the Taylor crime.

In June 1994, Ms. Taylor was found in her bathtub, strangled by a dog leash. She had been sexually assaulted and brutally beaten. Dewey initially came under suspicion for the crime when an acquaintance of his told police that he had been in Taylor's apartment at the time of the murder, but had been hiding in a closet (she later retracted the statement). Dewey admitted that he had been in Taylor's apartment before and had once shaved his beard there. He also gave a false name to police, apparently because he was trying to hide from authorities for unrelated issues.

When police discovered a shirt of Dewey's that had bloodstains on it, they were even more suspicious. The primitive DNA testing at the time showed the blood to be consistent with Dewey's and Taylor's, though the analyst at the time noted that it would probably be consistent with about 45 percent of the population.

DNA testing on evidence from the victim's home, meanwhile – including a semen stain and evidence from under Taylor's fingernails – was clearly not from Dewey. At the time, prosecutors decided it must have been from a second perpetrator whom they couldn't identify, and they went ahead with Dewey's trial on the assumption that he had attacked Taylor along with another unidentified man.

Dewey has maintained his innocence from the beginning. At his sentencing, when then-Mesa County District Judge Charles Buss reportedly told Dewey that "I am happy to impose [a life sentence] on you," Dewey replied, "There's still a killer out there."

The Colorado program that worked with the Innocence Project to retest the evidence was established with a federal grant from the Department of Justice. A joint program through the Colorado Attorney General's Office and the Denver District Attorney's Office, it is dedicated to reviewing some 5,000 rape, murder, and manslaughter cases in which DNA analysis might help identify wrongfully convicted individuals. So far, this is the first exoneration under the program.

Having the cooperation of the prosecutors was key in Dewey's exoneration, says Kreag. "They were convinced of Mr. Dewey’s guilt and they obviously believed in their case," he says. "But they were totally open to going where the evidence took them, and without their willingness to do that, we could have been in for several years of litigation to get to where we are today.... When prosecutors are willing to cooperate with defense, we can get to the truth much quicker."

When Dewey walks out of the courthouse, however, he'll leave with few resources. Colorado is one of about half the states that has no legislation providing compensation or services for wrongfully convicted individuals. As an exoneree, Dewey won't even have access to reintegration services provided to most paroled criminals.

In recent years, "public recognition of the need for immediate services and overall compensation for the wrongfully convicted has grown tremendously," says Stephen Saloom, policy director of the Innocence Project. But in times of tight budgets, he adds, public opinion often isn't enough.

Mr. Saloom says he hopes that cases like Dewey's lead to broader changes in how cases are prosecuted.

We need "the legal system to appreciate before, during, and after a trial that we can and do get it wrong," he says. "And we need to very closely consider the quality of evidence we use to determine the person's guilt or innocence."